AC electrical power units or devices are provided with a plurality of resistive loads, such as incandescent lamps, thermal fuses, etc. In general, the resistive AC loads are connected with AC power supplies through mechanical switches or electronic switches. The switches are turned off at other times and only turned on when used to connect the resistive AC loads and the AC power supplies. During the use, filaments or thermal fuses of the resistive AC loads are susceptive to short circuits due to vibration or aging or other reasons. When the resistive AC loads are in the short-circuit condition, large current occurs when the power supplies are switched on and hence switches or controllers are easy to burn out so as to result in tripping and even safety incidents in severe cases. As currently available mechanical switches or electronic switches have no function of providing short-circuit detection and protection for the resistive AC loads, it is necessary to provide a method, a device and a switch for providing short-circuit protection for the resistive AC loads on the premise of guaranteeing the safety of the switches and circuits.